Composition, weathering, and provenance of beach sands adjacent to volcanic rocks in the northern Gulf of Guinea, SW Cameroon

Abstract

The southern coastal portion of the Tertiary Cameroon Volcanic Line (CVL), in the Gulf of Guinea, is bordered by Pan-African granitoids, metamorphic rocks, and Cretaceous sedimentary successions, which are prone to contribute sediments to the nearby Limbe beach. To better constrain the weathering intensity and provenance of the beach sediments, the mineralogy and chemical composition of these sediments were analyzed. The low values of SiO2/Al2O3 ratios and Zircon-Tourmaline-Rutile (ZTR) index, coupled with high Index of Compositional Variability (ICV) indicate compositionally immature sediments. This is further supported by the presence of rock forming minerals such as olivine, pyroxene, and amphibole. The Th/Sc versus Zr/Sc binary and Al2O3–TiO2–Zr ternary diagrams suggest that the studied sediments have not experienced recycling. The Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), the A–CN–K and (A-K)-C-N triangular diagrams indicate that the Limbe beach sediments were undergone moderate to intense weathering. Several provenance discrimination diagrams based on Al2O3, TiO2, Zr, TiO2, La/Sc, and Th/Co, and the ternary plot of V–Ni–Th*10, and the comparison of chondrite normalized rare earth elements (REE) patterns of the studied sediments with potential source rocks suggest that the source area is composed of mafic rocks of CVL. This indicates that the granitic, metamorphic, and sedimentary rocks close to the volcanic structure do not significantly contribute to the sedimentation of the studied beach. In addition, the results of this study indicate that longshore currents do not influence the chemical composition of the sediments.